1. Field of the Invention
The present invention relates to a hollow golf ball having a concentric spherical inner cavity.
2. Related Art
Solid golf balls, such as two-piece golf balls, three-piece golf balls, etc. are usually produced by a process which comprises compression or injection molding for enclosing a solid core with a cover material and for forming dimples on the cover material, and finishing processing such as coating, mark stamping, etc. In this case, a solid core lacking an inner cavity has conventionally been used as a core of the solid golf ball.
The present inventors have conceived a new structure of a golf ball which includes a hollow core having a spherical inner cavity and a cover formed on the outer surface thereof, and have reasoned that with this structure, the mass of the golf ball is concentrated at its outer peripheral portion, and consequently, the moment of inertia of the golf ball during travel considerably increases, so that spin motion during travel continues for a longer period of time, resulting in increased travel distance. Based on the above-described concept, the present inventors conducted a study in order to obtain such a hollow golf ball.
As a result, the present inventors found that since the impact resistance of a hollow core having a spherical inner cavity is lower than that of a solid core, when the golf ball is hit, the hollow core is broken due to an impact acting on the golf ball if only the outer surface of the hollow core is covered with a cover material. They also found that if the material of the hollow core does not have a proper specific gravity, the hollow core cannot have proper degrees of hardness and resilience, resulting in decreased travel distance.